Hi, I'm having the same problem on my newly acquired b6 a4 1.8t. However the headlights are not stock, the previous owner put in some aftermarket ones. I'm pretty sure it's these:

Audi B6 A4 Quattro 1.8T > Lighting > Headlights > ES#261520 B6 A4 Smoked Angel Eye Headlights - Halogen Housings - HXAUA4B6HL-AEB

but I'm thinking it's the same problem, moisture in the bulb holder, because when I wash the car that headlight fogs up.

So i'm just going out on a limb and assuming that I couldn't just purchase the above mentioned bulb holder from the dealership because of the aftermarket headlights, could I?

be a shame to have to buy a new set of headlights just because of that.. but I dunno maybe I can sand the contacts and shine them up or something.. I haven't had a chance to look yet.

 

I ended up not having to buy a new bulb holder or anything. It could be a similar issue where the contacts just overheat over time, and with the temperature of your halogens being aftermarket that could be the case. Pull the headlight and look on the back, see if any of the contacts melted the plastic a little. Mine melted so far through that the bulb holder was no longer touching the contacts on the actual headlight housing. See if that is the issue.

My fix was to use a soldering iron and melt the contacts back to their original position, I also used some scotch-brite and got the contacts nice and shiny again too. Mine won't overheat again because I fixed a separate issue dealing with the car alarm that left the blinkers running all night a few times. Hopefully if yours is having the overheating problem that it will stop. I doubt it's the condensation in the headlight, but then again I'm not familiar with your aftermarket headlights.

Good luck.

 

Thanks for the input, I don't think it's overheating because I've got HID's in the low beam and I don't use the high's much, though I'm not sure about the previous owner. I get out of the bush in 5 days or so, so I'll be able to have a look and see if something's melted in there.